1. Field of the Invention
The present invention pertains to a method of detecting the presence of a non-visible marker dye in aged or dirty gasolines using a multi-step solid phase extraction process and elution with a solvent after reacting the marker dye with a color-forming reagent.
2. Background
My U.S. Pat. No. 4,918,020, issued Apr. 17, 1990, discloses and claims a method of detecting the presence of a commercial marker dye known as Marker MP or Mortrace MP and available commercially from Morton International, Inc., Patterson, N.J. Marker MP or Mortrace MP marker dye is used in motor gasolines and similar hydrocarbon fuels as a tracer to detect trademark violation or tax evasion techniques. Although the method set forth in the above-mentioned patent uses solid phase extraction (SPE or sorbent extraction) to selectively extract the dye from gasoline samples, it has been determined that aged gasolines or "dirty" gasolines, that is gasolines which are produced from poor quality refinery processes, cannot normally be adequately analyzed using this technique or the commercial technique provided by Morton International.
However, in accordance with the present invention, a unique solid phase extraction process has been developed which will detect the presence of a marker dye such as Marker MP or Mortrace MP in dirty and aged or "brown" gasolines, in particular. Accordingly, the invention overcomes the above-noted deficiencies in known solid phase extraction methods as well as the commercial liquid/liquid extraction technique wherein both prior art methods include the steps of adding a color-forming reagent to the extractant to form a colored complex and then determining the color intensity of the colored complex as an indication of the concentration of the marker dye.
A somewhat related discovery is disclosed in my patent application entitled "Method for Detecting a Marker Dye in Aged Petroleum Distillate Fuels" filed of even date herewith Ser. No. 08/007,412 pending.